Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure.

Coal is composed primarily of carbon along with variable quantities of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Not only does coal provide electricity, it is also an essential fuel for steel and cement production, and other industrial activities.

China is currently the top producer of coal (BP Statistical Review of World Energy, 2008). Coal production in China is focused mainly in the eastern provinces of Anhui, Guizhou, Hebei, Heilongjiang, Henan, Inner Mongolia, Liaoning, Shandong, and Shaanxi.

The United States holds the world's largest estimated recoverable reserves of coal and is a net exporter of coal. In 2012, nation's coal mines produced more than a billion short tons of coal, and more than 81% of this coal was used by U.S. power plants to generate electricity. In 2011, the amount of coal produced at U.S. coal mines was 1,094.3 million short tons.

Coal is mined in 25 states. Wyoming mines the most coal, followed by West Virginia, Kentucky, Pennsylvania, and Texas. ost of the electricity in the United States is produced using steam turbines. In 2012, coal was used for about 37% of the 4 trillion kilowatthours of electricity generated in the United States.